In the past, vehicle brakes were commonly of the drum/shoe design, having a pair of opposed arcuate brake shoes having a friction material disposed thereon within a hollow cylindrical drum. When the shoes were expanded, the friction material contacted an inner race of the drum to slow and/or stop the vehicle. In these designs, a relatively simple lever-actuated parking brake could be easily incorporated. However, with the advent of disc brakes, incorporation of a parking brake in the vehicle became more difficult.
One conventional design for a parking brake for disc brakes is known as a “drum-in-hat” assembly. Commonly, the rotating portion of a disc brake is known as a “top hat”, which comprises an annular inner portion which is bolted to a vehicle hub, a generally cylindrical joining portion extending axially of the hub, and the brake rotor or disc itself, joined to the hub by the joining portion. According to the drum-in-hat parking brake design, the top hat has a conventional drum assembly incorporated therein, such as within the cylindrical joining portion of the top hat, wherein the inner surface of the joining portion is used as the drum, or even where a discrete drum is formed integral with the top hat at an inner portion thereof. U.S. Pat. No. 6,484,852 to Bunker and U.S. Pat. No. 6,729,444 to Schmandt et al. propose drum-in-hat parking brake designs. However, the complexity of drum-in-hat designs results in increased cost of manufacture, and somewhat poor reliability in the long run.
Integral disc brake calipers have been devised in the past and these typically have involved a hydraulic service brake actuator including a hydraulically driven piston, and a parking brake actuator which acts through a suitable mechanism to drive the piston in the manual parking brake mode. The arrangement is such that the hydraulic actuator is operable to shift the piston outwardly of a piston cylinder in which it is disposed, to engage a disc brake pad and to push the pad into engagement with the disc rotor. In some designs, engagement of the brake pad with the disc rotor can cause a second brake pad disposed on the opposite side of the rotor to shift into engagement with that side of the rotor and thus the rotor becomes sandwiched between the brake pads, producing a braking effect.
The parking brake actuator in such calipers is operable to produce the same movement of the disc brake pads to sandwich the rotor and in the known arrangements, the parking brake actuator has been operable to displace the service brake piston into engagement with the respective brake pad. To achieve that displacement, the parking brake actuator has been disposed within or partly within the cylinder which houses the service brake piston, to act on the piston when the parking brake is to be actuated. In this type of arrangement, the construction of the caliper can be quite complicated in order to accommodate the parking brake actuator partly or fully within the service brake piston cylinder and in particular, the complicated nature of the caliper arises somewhat because accommodation of the parking brake actuator in the piston cylinder introduces at least an additional leakage path, increasing the likelihood of leakage from the piston cylinder. Because there is a need to properly seal against the increased likelihood of leakage this invariably complicates the construction and reliability of the caliper.
Several designs have been proposed to address one or more of the above-mentioned drawbacks, problems, or limitations of parking brakes for disc brake equipped vehicles.
For example, U.S. Pat. No. 6,851,761 to Baumgartner et al. proposes a control process that can be carried out during parking braking by way of a parking brake arrangement. The brake is applied by way of a service brake cylinder, and a position of a piston rod is fixed by rotation of a self-locking rotating spindle and application of the rotating spindle to the piston rod or an element connected in front of the piston rod. By additionally rotating the rotating spindle during parking braking, compensation can be made for shrinkages, particularly of a brake disc and/or brake linings, which occur during brake cooling.
U.S. Pat. No. 7,455,152 to Wang proposes a disc brake caliper for use with a disc brake rotor having a first side and a second side. The caliper further includes a first mounting portion and a second mounting portion each positioned adjacent one side of the disc brake rotor. The caliper further includes brake pads disposed adjacent the respective mounting portions such that brake pads are on opposite sides of the disc brake rotor and in facing relationship therewith. Further, the disc caliper includes a hydraulic service brake actuator and an electric parking brake actuator, each of which is operable independently of the other. Each of the actuators is arranged for actuation against a second side of the first brake pad for displacing the first brake pad away from the first mounting portion and into engagement with the disc brake rotor. The hydraulic service brake and the electric parking brake actuators have positions of actuation on the second side of the first brake pad at positions spaced apart.
U.S. Pat. No. 7,559,413 to Haffelder et al. proposes an automatic parking brake, including a brake piston, an auxiliary piston, a hydraulic chamber disposed between the brake piston and the auxiliary piston, a spring element, for pre-stressing the auxiliary piston, a spindle device connected to the auxiliary piston via a threaded connection, and a drive for the spindle device, wherein in a locked state of the parking brake, the brake piston is mechanically locked via the spindle device and the spring-loaded auxiliary piston, and in a released state of the parking brake, the auxiliary piston is blocked by means of the spring element and/or by means of the spindle device.
U.S. Pat. No. 7,753,178 to Ohtani et al. proposes a disc brake with a parking brake mechanism capable of exerting a large piston thrust required for operating a parking brake, without adversely affecting operation of a service brake. A parking brake mechanism, which is driven by an electric motor provided outside a housing, is incorporated in a caliper in which a piston is slidably disposed in a cylinder. The parking brake mechanism is slidably fitted via a seal member into the piston and provided with a nut member that is prevented from rotating relative to the piston by engagement of a pin and a pin hole; and a shaft that is screwed into the nut member. During a service brake operation, the piston alone is moved by a hydraulic pressure under a small piston thrust. During a parking brake operation, the piston and the nut member are moved together by applying a hydraulic pressure and operating the electric motor at the same time, to exert a large piston thrust, by using a large pressure receiving area of the piston and the nut member combined.
U.S. Pat. No. 8,091,689 to Tristano et al. proposes an automatic parking brake acting on a disc brake and in which the piston of the brake comprises a cavity in which there is a spring allowing pressure to be applied to the end of the piston cavity. A washer is positioned between the inlet of the cavity and the spring. A pressing device allows pressure to be applied to the washer so that it preloads the spring.
U.S. Published Patent Application No. 2009/0133973 to Shibata proposes a parking brake apparatus including a first braking member provided at a wheel and integrally rotated with the wheel, a second braking member provided at a vehicle body side for stopping a rotation of the first braking member, a parking brake device for pressing the second braking member to the first braking member by an operating force of a parking brake operation, a pressurizing device for pressurizing a brake fluid independently of the parking brake operation, and a hydraulic pressure controlling device for preliminarily pressing the second braking member to the first braking member by a brake fluid pressure pressurized by the pressurizing device in a case when the second braking member is pressed to the first braking member by means of the parking brake device.
However, despite recent advances, there remains an unmet need in the art to optimize disc brake calipers employing integral parking brakes to improve the cost, performance and reliability thereof.